import time


a = 99
start_time = time.time()
print('开始时间：{}'.format(start_time))
while True:
    if time.time() - start_time > 3:
        a = 0

        print('已过{}秒没有变化！'.format(time.time()-start_time))
        start_time = time.time()
        print('跳出')
        break
